This invention relates to an improvement of tire forming drums suitable for forming bands formed by tire constituent members such as inner liners, chafers, plies affixed to each other or green cases produced in primary forming in producing processes mainly for passenger car tires.
In order to improve the productivity of tires, it has been expected to realize a tire forming drum for forming bands or green cases, which is capable of rapidly conforming to change in diameters of tire constituent members to be wrapped around the drum and hence to change in tire rim diameters. In reply to this expectation, various kinds of forming drums have been proposed, which include a plurality of segments arranged around a main shaft and radially movable toward and away from the main shaft and further having circular arc surfaces on which a tire constituent member is wrapped, as disclosed in, for example, Japanese Patent Application Laid-open Nos. 60-196,330 and 60-68,929.
With such proposed forming drums, there are provided means for filling clearances occurring between the adjacent segments when they move. The means for this purpose cannot help being thin plates due to the construction of the drum so that they are generally poor in strength tending to be deformed and damaged in a short period of time. What is worse still, as thin plate members are likely to curve with constant radii of curvature, when the diameter of the drum is largely changed in a broader range, the curvatures of the plate members do not coincide with the curvature of the drum to cause a member wrapped therearound to be deformed at the positions of the plate members.
In another tire forming drum disclosed in U.S. Patent Specification No. 3,873,398, rubber bands are arranged on all the circumference of a drum to fill clearances occurring between adjacent segments moved in accordance with a required drum diameter. In such a known forming drum, however, it is difficult to obtain a broader range of tire rim diameters in which the drums can be commonly used. Moreover, there is a risk of bands and green cases being deformed so that sufficiently high quality tires can not be produced.